Process of curing butadiene polymers in the presence of a hydrocarbon diluent and di-tertiary butyl peroxide



PROCESS OF CURING BUTADIENE. POLYMERS IN TH PRE5ENCE. OF A. HYDRQCA B DILU- EN A RT AR B T L. PE XIDE Anthony H. Gleason, Westfield, N.J., assignor to Esso, Research and Engineering Company, atcqrporatiqn of Delaware No Drawing. Application November 24, 1954 Serial No, 471,095

This invention relates to. the production. of synthetic resinous. materials which are completely insoluble, infusible, hard masses possessing good. machineability, good dielectric properties, and lowmoisture permeability.

It has been shown in application Serial No. 334,356, filed January 30, 1953, now US. Patent 2,772,254, that polymers and copolymers of butadiene can. be cured in the presence of ditertiary butyl peroxide at temperatures from 100 to 175 C. The products are characterized by. having superior electrical properties and high ASTM' distortion temperatures. A serious drawback in the use of such resins is that they are too permeable'to moisture vapor for some purposes, being three to four times that for polyethylene and styrene-isobutylene copolymers.

It is the main object of the present invention to overcome these disadvantages of the above resins from butadiene and to provide a method for preparing such resins having low moisture permeability values suitable for electrical purposes.

These. and other objects of this invention are accomplished by heating the polymersof butadiene or copolymers of butadiene and: styrene at temperatures from 100 to 175 C. in the presence of 1.5 to 5% or more of ditertiary butyl peroxide and 5 to. 20% of an inert,

predominantly aliphatic or naphthenic hydrocarbon diluent boiling above 200 C., preferably between 300 and 600 C. Suitable oils include white mineral oils and paraffin wax.

The polymers to which the present invention are Primarily pp icabler th se pr pared y copolymerizing 100. to 50 parts of butadiene-1,3 and to. 50 parts of styrene with an alkali metal catalystsuch as sodium. A particularly suitable polymer is an oily copolymer of 75 to 85% butadiene, and 15 to 25% styrene. The polymerization is carried out in a reaction diluent at temperatures ranging from about 25; to 95 C., or preferably between 40 and 90 C., and is desirably continued until complete conversion of monomers is obtained. About 1.2 to parts, preferably 1.5 to 4 parts, of finely divided metallic sodium per 100 parts of monomers are used as catalysts. Materials used as diluents in the polymerization are inert hydrocarbons which fzremain liquid under the reaction conditions employed. Accordingly, the diluents employed have a boiling" point between about and 200 C., the low boiling diluents being useful where it is feasible to keep the' reaction' pressure sufliciently high to maintain the diluent in liquid condition at the reaction temperature used.

Preferred diluents are essentially aliphatic hydrocarbons such as naphtha having a boiling range between about 90 and 120 C., or straight-run mineral spirits such as Varsol having a boiling range between about 150 and 200 C. Butane, benzene, cyclohexane, toluenes, pentanes and similar inert hydrocarbons are also useful, individually or in admixture with each other. The hydrocarbon diluents are used in amounts ranging from 100 to 500, preferably 150 to 300 parts per 100 a United Patent ofi excess solvent.

M parts of monomers. In other words, the resulting oily composition assynthesized normally contains about20 to 5.0% of; the polymer dissolved in a hydrocarbon solvent. When desired, more concentrated compositions can be produced from the synthesis product by stripping For purposes of the present invention, it is desirable to concentrate non-volatile matter to at least 90 and preferably 100%. The presence of solvent is unnecessary and is undesirable except in small amounts.

Furthermore, to promote the original polymerization reaction and to assure the formation of a light colored product, it is also desirable to employ in the polymerization about 10- to 40- or more parts of an ether promoter per parts of monomers. Cyclic diethers of 4 to 8 carbon atoms having an OC--CO-- group, such as dioxane-1,4 and its methyl and ethyl homologues, have been found as particularly effective promoters. Other suitable ether promoters are aliphatic monoor di-ethers of 4 to 8 carbon atoms, such as diethyl ether, diethyl ether of ethylene glycol, and diethyl ether. of diethylene glycol. Finally, it is also beneficial in many cases, although not essential, to useabout 5 to 35v weight percent (based on sodium) of an alcohol such as methanol, isopropanol or n-amyl alcohol, especially where the sodium catalyst particles are relatively coarse.

The resulting pro-duct may vary from a low viscosity oil to a solid high molecular weight polymer and the invention is equally applicable to any such product of Whatever intrinsic viscosity.

The present invention is based on the discovery that when products of the nature described above are cured in the presence of 5 to 20% of an inert, predominantly aliphatic or naphthenic hydrocarbon diluent boiling above 200 C., preferably between 300 and 600 C., at a temperature of-100-250 C., the moisture vapor permeability of the resin is lowered to a value suitable for the most exact electrical requirements. The curing may be carried out in the presence or absence of a catalyst such as 1.5 to 5% of t-butyl peroxide.

The schedule may be lengthened somewhat depending on the hardness and distortion temperature desired in the resin, but a stepwise increase in curing temperature is desirable both as a means of controlling the rate of I polymerization and to. minimize mold adhesion. Too

rapid curing can cause the castingsto crack as a result of inadequate dissipation of the heat of reaction.

When no catalyst is used temperatures of 200-2501 C must be employed and the diluent must boil above 250 C., the maximum temperature of cure. A typical schedule is as follows:

24 hours at 210 C. 24 hours at 225 C. l or more days at 240-250. C.

Fillers such as mica, asbestos, silica, dicolite, etc. may be used to increase impact strength, improve the thermal conductivity, and shorten the curing time of these resins.

The resins obtained by the process of this invention have excellent dielectric properties. The dielectric constant is about 2.5 and the dielectric strength is about 800 volts per mil. They are not thermoplastic and must be cast or machined to the desired shape. The specific gravity is in the range of 0.99 to 1.01 depending on the cure. Distortion temperatures may range up to 150 C. and higher. Under no load the resin possesses considerable form stability at temperatures above the distortion point. At a medium cure the resin will have a Rockwell-M hardness of about 100. The impact strength is adequate for commercial usage. The resin machines fairly well if sharp tools are used, giving cuttings which are fine and powdery.

The following examples illustrate the benefits to be obtained by the process of this invention.

Example I An oily copolymer of butadiene and styrene was prepared according to the following recipe:

Parts by wt. Butadiene 80 Styrene 20 Naphtha 200 Dioxane 30 Sodium 1.5 Isopropanol 0.3

Temperature, 50 C.

Complete conversion was obtained in eight hours. The catalyst was destroyed and removed from the resulting crude product. The product was finished to contain 100% non-volatile matter as described above.

Example II 18 hours at 105 C. 24 hours at 115 C. 24 hours at 125 C. 24 hours at 135 C. 48 hours at 150 C.

The resulting resins were tested for moisture permeabilrty (g./100 sq. 1n./ mil/ day) according to ASTM tentat1ve procedure D988-48T with the following results:

Rock. Rock. Hydrocarbon Diluent Amt... Hm-d. Hard. MVP 6 Percent 3% 4% DTBP DTBP Parafiin wax (boiling 200 0. at

15 mm. Hg to 235 C. at 1.0

mm 10 57 80 2. 6 Paraffin wax (boiling 200 0. at

15 mm. Hg to O at 1.0

mm. 2) 15 X 84 2.3 Lubrieating oil 1 (boiling 200 to 350 C at 10 mm. Hg) 15 56 2.7 Phenol ext. (boiling 200 to 350 C. at 10 mm. Hg 15 Whit oil (boiling 200 to above 350 C. at 10 mm. Hg) 2.4 White 011 l (boiling 200 to above 350 0. at mm. 10 90 100 2.2 White oil 3 (boiling 200 to above 350 0. at 10 mm. Hg) 16 80 99 2.0 Control 100 106 7 3. 2 Polythen 1. 1 S-polyrner 4 1. 0

1 Oil containing approximately 20% aromatic compounds.

i Phenol extract of a mineral oil predominately aromatie. White mineral oil predominately paralliule and nuphthenic. Copoiymer of styrene and isobutylene.

5 Too soft to be measured. i g. lilo/100 inf/24 hours/mil.

, 1 An average of tour values.

The above data show that the white oil which is predominately paraflinic and naphthenic is superior to the more aromatic oils and waxes in decreasing the moisturevapor permeability. With respect to the effect on cure, white oils are the best; wax is intermediate and aromatic oils are the poorest. Thus it can be seen that the white oil and wax are suitable from these two standpoints; the white oil being preferred' If the Rockwell hardness is not critical for the intended application, then lubricating oils of low aromaticity may be suitable. The lubricating oil containing 20% aromatics reduces the cure to a greater-- extent than the white oil or wax.

While the above examples are limited to copolymers of butadiene and styrene, the parafiinic oils would decrease the moisture-vapor permeability of polybutadiene to the same extent and would give an even harder resin for the same curing schedule.

The nature of the present invention having been thus fully set forth and specific examples of the same given, what is claimed as new and useful and desired to basecured by Letters Patent is:

1. A process for preparing a solid infusible resin from a polymer chosen from the group consisting of homopolymers of butadiene-1,3 and copolymers of butadiene- 1,3 with up to 50% styrene which comprises heating the polymer for three to five days at a temperature between 100 and 175 C. in the presence of 5 to 20% of a predominantly parafiinic and naphthenic hydrocarbon diluent boiling above 200 C. and 1.5 to 5% of ditertiary butyl peroxide.

2. Process according to claim 1 in which the polymer is polybutadiene prepared by polymerizing butadiene in the presenceof an alkali metal catalyst.

. 3. Process according to claim 2 in which the catalyst is sodium.

4. Process according to claim 3 in which the hydrocarbon diluent is a white oil.

5. Process according to claim 1 in which the copolymer is an oily copolymer of to butadiene and 15 to 25% styrene prepared in the presence of an alkali metal catalyst.

6. Process according to claim 5 in which the catalyst is sodium.

7. Process according to claim 6 in which the hydrocarbon diluent is a white oil.

References Cited in the file of this patent UNITED STATES PATENTS Rostler et a1. Apr. 27, 1948 McMillan et al Aug. 11, 1953 OTHER REFERENCES we; I 

1. A PROCESS FOR PREPARING A SOLID INFUSIBLE RESIN FROM A POLYMER CHOSEN FROM THE GROUP CONSISTING OF HOMOPOLYMERS OF BUTADIENE-1,3 AND COPOLYMERS OF BUTADIENE1.3 WITH UP TO 50% STYRENE WHICH COMPRISES HEATING THE POLYMER FOR THREE TO FIVE DAYS AT A TEMPERATURE BETWEEN 100 AND 175*C. IN THE PRESENCE OF 5 TO 20% OF A PREDOMINANTLY PARAFFINIC AND NAPHTHENIC HYDROCARBON DILUENT BOILING ABOVE 200*C. AND 1.5 TO 5% OF DITERTIARY BUTYL PEROXIDE. 